Name: how temperature changes create stress
Uploaded: 2023-04-30T12:29:32.000Z
Duration: 1 min 9 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry

CHEM.13

CHEM.13.D

Thermal Stress

Un corps subit un stress lorsqu’il subit des variations de température, ce stress est connu sous le nom de stress thermique, qui peut même déformer durablement le corps.
Par exemple, un espace est intentionnellement maintenu entre deux joints d’une tige sur la voie ferrée pour éviter la déformation ou la flexion des tiges.
Pour calculer la contrainte thermique dans un objet, déterminez d’abord la dilatation ou la contraction thermique, puis calculez la contrainte.
Considérons une tige de longueur L0.. Lorsque de la chaleur est appliquée, la tige augmentera en longueur de delta 'L' et la variation fractionnaire de la longueur de la tige peut être évaluée.
Maintenant, la même tige est fixée aux deux extrémités. Lorsque la chaleur est appliquée, la tige subit une tension car elle ne peut pas se dilater. Pour restaurer la longueur d’origine de la tige, la contrainte peut être calculée.
Si l'on se souvient de la définition du module de Young, il s'agit du rapport entre la contrainte et la déformation.
Par conséquent, la contrainte thermique peut être déterminée en combinant les équations et en réarrangeant les termes.

<ol>
	<li>OpenStax. (2019). Physique universitaire Vol. 2. [Version Web]. Récupéré de <a href="https://openstax.org/details/books/university-physics-volume-2">https://openstax.org/details/books/university-physics-volume-2</a> ; p. 18 et 19.</li>
</ol>

contrainte thermique

Si la température d'un objet change tout en étant empêché de se dilater ou de se contracter, l'objet est soumis à une contrainte. La contrainte est compressive si l'objet se dilate en l'absence de contrainte et est de traction s'il se contracte. Cette contrainte due au changement de température est connue sous le nom de contrainte thermique. Elle peut être assez importante et causer des dommages. Pour éviter cette contrainte, les ingénieurs peuvent concevoir des composants de manière à ce qu'ils puissent se dilater et se contracter librement. Par exemple, sur les autoroutes, des espaces sont délibérément laissés entre les blocs pour éviter le développement de contraintes thermiques. Lorsqu'aucun espace ne peut être laissé, les ingénieurs doivent prendre en compte la contrainte thermique dans leurs conceptions. Ainsi, les barres d'armature en béton sont faites d'acier car le coefficient de dilatation linéaire de l'acier est presque égal à celui du béton.

La contrainte thermique peut expliquer de nombreux phénomènes, tels que l'altération des roches et des chaussées par l'expansion de la glace lorsqu'elle gèle. Les voies ferrées et les routes peuvent se déformer les jours chauds s'ils ne possèdent pas suffisamment de joints de dilatation, et les lignes électriques s'affaissent davantage en été qu'en hiver et se rompent par temps froid s'il y a un manque de jeu. Des fissures s'ouvrent et se referment dans les murs en plâtre lorsque la maison se réchauffe et se refroidit. Les plats de cuisson en verre se fissurent s'ils sont refroidis rapidement ou de manière inégale en raison de la contraction différentielle et des contraintes qui en résultent.

Contrainte thermique

Si la température d’un objet est modifiée alors qu’il est empêché de se dilater ou de se contracter, l’objet est soumis à des contraintes. Le stress est...

Education

Enseignement

JoVE Core

Physics

Physique

Unit 1

Unité 1

Temperature and Heat

Température et chaleur

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

how temperature changes create stress

Thermal stress is the stress that builds up when an object changes temperature but cannot expand or contract freely. If the object would expand without restraint, the stress is compressive. If it would contract, the stress is tensile.

This stress from heating or cooling can become large enough to cause damage. Engineers often reduce it by designing parts so they can move as temperature changes. Highway blocks, for example, are separated by gaps so thermal stress does not build up.

When gaps are not possible, thermal stress must be part of the design. In concrete, the reinforcing rods are made of steel because steel and concrete have nearly the same coefficient of linear expansion. That similarity helps the materials change length at nearly the same rate.

Thermal stress also explains many everyday and natural effects. Ice can weather rocks and pavements as it freezes and expands. Railroad tracks and roadways may buckle on hot days if they do not have enough expansion joints, and power lines can sag more in summer and snap in cold weather if they lack slack.

The same idea helps explain cracks that open and close in plaster walls as a house warms and cools. Glass cooking pans can crack if they cool too fast or unevenly. In each case, different contraction or expansion creates stress in the material.

How Temperature Changes Create Stress

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thermal stress

Thermal stress is the stress that builds up when an object changes temperature but cannot expand or contract freely. If the object would expand without restraint, the stress is compressive. If it would contract, the stress is tensile. This stress from heating or cooling can become large enough to cause damage. Engineers often reduce it by designing parts so they can move as temperature changes. Highway blocks, for example, are separated by gaps so thermal stress does not build up. When gaps...

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key terms and concepts

Learn how heating and cooling create compressive or tensile stress, why expansion joints matter, and how thermal stress affects roads, wires, walls, and glass.

How Temperature Changes Create Stress | JoVE K12

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How Temperature Changes Create Stress

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